Disturbances are relatively discrete events in time that disrupt the ecosystem, community, or population structure and bring about a change in resources, substrate availability, or the physical environment (White & Pickett 1985). On the basis of previous studies (e.g. White & Pickett 1985; Runkle 1985), White et al. (1999) noted that the "disturbance regime" of a vegetation system, which is the sum of all disturbances affecting the system, can be characterized by several parameters: kind, spatial characteristics, temporal characteristics, specificity, magnitude and synergisms. Kind refers to the type of disturbances, which vary with climate, topography, substrate and biota. Spatial characteristics are the area, shape, and spatial distribution of patches created by disturbances. Temporal characteristics are the frequency, return interval, cycle, and rotation period of disturbances. Specificity is the correlations between a type of disturbance and specific characteristics of disturbed sites, such as species, size class, seral stage and location. Magnitude includes the intensity (the physical force per event per area per time) and severity (the impact on organisms and ecosystem structure and composition) of disturbances, and generates patch variations, internal heterogeneity and biological legacies. Synergisms are the interactions among different kinds of disturbances. 

It has been suggested that it is impossible to define natural vegetative disturbance regimes in a strict sense, given a changing climate and resultant shifts in disturbance regimes over the past several centuries (Sprugel 1991). Non-equilibrium ecological views are largely based on inevitable ecosystem changes linked with climate instability (Sprugel 1991). Landres et al. (1999) also stated that no a priori time period or spatial range should be used to define "natural variability," which is spatio-temporal ecosystem variability driven by disturbances. However, with respect to conservation practices, the term "natural" often means "without human influence" (Hunter 1996). In restoration ecology, resource management and ecosystem approaches, the term generally refers to ecological variations after excluding anthropogenic effects. Thereby, although climate instability significantly alters vegetation structures and disturbance regimes, it should be embedded in disturbance-based management issues. In my studies, natural disturbance regimes are thus referred to in a broader sense by accepting climatic effects on disturbance regimes as a natural driver. 

Natural disturbances sometimes bring "surprise" to human society. For instance, in the case of terrestrial ecosystems, infrequent catastrophic events such as typhoons, hurricanes, cyclones, forest fires, volcanic eruption, and avalanches may thoroughly destroy ecosystems and landscapes. At first glance this may seem like devastation, which in reality it could be giving rise to many diverse habitats to various creatures, promoting natural ecological processes. There is no single trajectory of long-term ecosystem regeneration process, producing heterogeneity and diversity in terrestrial systems (Mori 2011a).

In the past and even currently we may try to build watercourses in order to suppress or redirect floods to agricultural land. This action sometimes have resulted in further catastrophe such as massive drought and flooding, which in turn threatened biota in some areas, as well as an outbreak of algae bloom due to nutrient loadings from agricultural drainage. Thus, strong impacts on human society can be seen from trying to suppress natural disturbances, in many cases leading to a tit for tat situation so to speak (Mori 2011b). Therefore, lately it is thought important to promote natural disturbances rather than suppress them to bring necessary changes to ecosystems.

As natural events that strongly impact human society bring us "surprise", they are often perceived as "disaster". However, changes are ubiquitous in nature. The ability of ecosystems or social-ecological systems to cope with such changes and impacts is called "resilience". The ecological resilience originally defined as the amount of disturbance that a system can absorb without shifting into a different state (Holling 1973). In managing social-ecological systems and ecosystems, which are prone to changes, it is useful to evaluate the ability of an ecosystem to cope with disturbance-driven changes (Gunderson 2000; Folke et al. 2004). Currently, it is thought that resilience includes the ability of a system to restore itself after a disturbance. In resilient systems, disturbances are promoted to foster necessary changes (Chapin et al. 2009). The definition of resilience is continually evolving. The important thing to pay attention to here is that an ecosystem is not always restored to the same ecosystem that it was before disturbance (Mori 2011a). Just focusing on returning to its original state is not a management approach to cope with changes. 

Ecosystems with great resilience have a strong tolerance and a powerful ability of restoring themselves after a disturbance. However, human activities such as deforestation, exploitation, pollution, global warming are thought to reduce resilience in a system, making it unable to absorb effects of disturbances that they used to be able to have before (Mori 2010b). The example of flood control in the previous paragraph shows that resilience can be eroded by human activity, resulting in many serious environmental problems. This teaches us that it is unnatural to consider ecosystems and human society separately; the concept of resilience therefore is also the ability of social-ecological systems to face changes. In other words, a society with greater resilience would have lesser confusion, damage and disaster relief payment, and could restore itself soon after massive natural disasters.

In Japan, although we lately sometimes hear the words, "reduce disaster" but we still tend to "prevent disaster". Of course it is necessary for us to prevent human disaster from happening, but it is impossible to eliminate natural disturbance completely. In some cases, such an attempt could bring more disaster (Mori 2011b). As it is impossible to control nature, it is important to consider how we will cope with surprises and changes triggered by natural disturbances in managing ecosystems (Mori 2011a, 2011b). 

Based on these reasons, my research is as follows:

1) Why do ecosystems need natural disturbance? 

2) What kind of problems occurred when natural disturbances were suppressed? 

3) How can we restore ecosystem integrity after misguided suppression of natural disturbances? 

4) How can we respect natural processes of ecosystems at the same time of unavoidable and necessary human disturbances such as deforestation? 

5) Based on these points how do we adapt "ecosystem management"? 

These are my current points of interest for my research.

 

References 

Chapin, F.S. III., Kofinas, G.P., Folke, C. (2009) Principles of ecosystem stewardship. Resilience-based natural resource management in a changing world. Springer, New York, USA. 

Folke C, Carpenter S, Walker B, Scheffer M, Elmqvist T, Gunderson L, Holling C.S. (2004) Regime shifts, resilience, and biodiversity in ecosystem management. Annual Review of Ecology, Evolution and Systematics 35:557-581. 

Gunderson, L.H. (2000) Ecological resilience: in theory and application. Annual Review of Ecology and Systematics 31:425-439. 

Holling, C.S. (1973) Resilience and stability of ecological systems. Annual Review of Ecology and Systematics 4:1-23. 

Hunter, M.L. (1996) Benchmarks for managing ecosystems: are human activities natural? Conservation Biology 10:695-697. 

Landres, P.B., Morgan, P. & Swanson, F.J. (1999) Overview of the use of natural variability concepts in managing ecological systems. Ecological Application 9:1179-1188. 

Mori, A.S. (2011a) Ecosystem management based on natural disturbances: hierarchical context and non-equilibrium paradigm. Journal of Applied Ecology 48:280-292. 

Mori, A.S. (2011b) Making society more resilient. Nature 484:284. 

Runkle, J.R. (1985) Disturbance regimes in temperate forests. In: The ecology of natural disturbance and patch dynamics (eds Pickett, S.T.A. & White, P.S.), pp17-34. Academic Press, New York. 

Sprugel, D.G. (1991) Disturbance, equilibrium, and environmental variability: what is 'natural vegetation' in a changing environment? Biological Conservation 58:1-18. 

White, P.S., Harrod, J., Romme, W.H. & Betancourt, J. (1999) Disturbance and temporal dynamics. In: Ecological stewardship: a common reference for ecosystem management (eds Johnson, N.C., Malk, A.J., Sexton, W.T., Szaro, R.), pp281-305. Oxford University, Oxford. 

White, P.S. & Pickett, S.T.A. (1985) Natural disturbance and patch dynamics: An introduction. In: The ecology of natural disturbance and patch dynamics (eds Pickett, S.T.A. & White, P.S.), pp3-13. Academic Press, New York.